This invention relates to new aromatic polyamide compositions containing a crosslinkable benzocyclobutene group.
Benzocyclobutene (BCB)-based polymeric materials have recently attracted growing attention and research interest in the area of structural and electronic applications because of the versatile chemistry of benzocyclobutene as well as the combined advantages of processability and properties. The cure chemistry of benzocyclobutene is based upon the propensity of the four-membered ring to undergo electrocyclic ring-opening at elevated temperatures (.about.200.degree. C.) to provide reactive o-quinodimethane that will undergo dimerization and polymerization, or react with an attendant dienophile to form a Diels-Alder adduct. ##STR3##
Research reports describing the synthesis and characterization of high-temperature BCB-based materials for potential structural and aerospace applications have already appeared. These heat-resistant thermosets, include, to name a few, homopolymerized bisbenzocyclobutene-terminated imide monomers and a variety of resins generated from Diels-Alder reactions of bisbenzocyclobutene-terminated imide monomers with monomers containing dienophilic end-groups such as acetylene, phenylacetylene and maleimide. Recently, the incorporation of the thermally reactive benzocyclobutene into the main chain of polymeric materials for lateral crosslinking has also been reported. The objective was to improve the compressive strength of high modulus fibers such as Kevlar.RTM. via the use of a latently crosslinkable monomer, 1,2-dihydrocyclobutabenzene 3,6-dicarboxylic acid
An important area of investigation is the use of BCB-based thermoset matrix resins in the preparation of thermosetting rigid-rod molecular composites. The solubility of the BCB-imide oligomers in methanesulfonic acid (MSA), the stability of the BCB ring in the strongly acidic medium and its excellent thermo-oxidative stability make this matrix an ideal candidate for the molecular composite study. The molecular-level reinforcement of the network structure, derived from bisbenzocyclobutene-terminated imide oligomers, by poly(p-phenylene benzobisthiazole) (PBZT) was investigated by examining coagulated films extruded from MSA solutions. The results of the morphological studies showed that phase separation had occurred during coagulation. One possible explanation was that the BCB oligomeric system, being of low molecular weight, was unable to provide sufficient entanglement around PBZT to preclude the occurrence of phase separation.
Accordingly, it is an object of this invention to provide a high molecular-weight, BCB-containing polymer that can serve as the crosslinkable thermoplastic matrix host for PBZT.
Other objects and advantages of the present invention will be apparent to those skilled in the art.